Previous studies on the participation of polyisoprenol-linked sugars in synthesis of hen oviduct membrane glycoproteins have documented the synthesis of mannosylphosphoryl-dolichol, and its involvement in synthesis of an oligosaccharide-lipid whose carbohydrate chain was shown to have the structure (alpha-Man) 4-6-Beta-Man-Beta-GlcNAc. Experiments with the isolated oligosaccharide-lipid demonstrated that the oligosaccharide chain could be transferred en bloc to endogenous membrane protein acceptors. Although one of the three endogenous glycosylated membrane proteins was identical to ovalbumin, by utilizing oviduct tissue slices and tunicamycin strong evidence has been obtained that polyprenol-linked saccharides are involved in glycosylation of ovalbumin. Recently, we have examined in more detail the early steps involved in assembly of the oligosaccharide-lipid. The formation of GlcNAc-, GlcNAc-GlcNAc-, Beta-Man-Beta-GlcNAc-GlcNAc- lipids has been established. Moreover, it has been shown that both the disaccharide-and trisaccharide-lipid can either be elongated to form oligosaccharide-lipid, or can be directly transferred to endogenous membrane protein acceptors. A major limitation of earlier studies was that the only polypeptide acceptors were endogenous membrane proteins. However, it is now known that several exogenous, soluble proteins can, after denaturation and disulfide bond cleavage, serve as acceptors. The minimal requirement for a protein to serve as an acceptor of an oligosaccharide chain from oligosaccharide-lipid is that it contain the tripeptide sequence -ASN-X-SER(THR)-. Current studies on the potential acceptor activity of proteolytic fragments of proteins containing this tripeptide sequence should cast further light on the specificity of glycosylation.